# poly
class Animal:
    def make_sound(self):
        # print('make xxx sound')
        pass
class Dog(Animal):
    def make_sound(self):
        print('wangwang...')
class Cat(Animal):
    def make_sound(self):
        print('miaomiao...')
class Brid(Animal):
    def make_sound(self):
        print('jiujiu...')

d = Dog()
c = Cat()
d.make_sound()
c.make_sound()
print('--------------------')
animals = [Dog(), Cat(), Brid()]
for item in animals:
    item.make_sound()
